1. Field of the Invention
The present invention relates to a touch panel used for operating various types of electronic devices.
2. Background Art
In recent years, various types of electronic devices such as a mobile phone and car navigation system have been increasingly equipped with a light-transmissive touch panel on the front surface of their display element such as a liquid crystal screen. The user of a device views and selects characters, symbols, and the like, which displayed on the display element is provided on the back surface of this touch panel through this touch panel. The user further selects each function of the device by pressing the touch panel with a finger, dedicated pen, or the like. Such a touch panel is demanded that provides reliable operation at low cost.
A description will be made for the conventional touch panel, using FIGS. 3 and 4.
FIG. 3 is a plan view of the conventional touch panel. FIG. 4 is a sectional view taken along line 4-4, of the touch panel shown in FIG. 3. In FIGS. 3 and 4, upper substrate 51 is film-like and light-transmissive. Lower substrate 52 is light-transmissive. The lower surface of upper substrate 51 is formed thereon with upper conductive layer 53 which is light-transmissive with a material such as indium tin oxide. The top surface of lower substrate 52 is also formed thereon with lower conductive layer 54 which is light-transmissive and is made with a material such as indium tin oxide.
The top surface of lower conductive layer 54 is formed thereon with a plurality of dot-shaped spacers (not illustrated) made from insulating resin, at given intervals. Both ends of upper conductive layer 53 are further formed thereon with a pair of upper electrodes (not illustrated). Both ends of lower conductive layer 54 are formed thereon with a pair of lower electrodes (not illustrated) orthogonally to the upper electrode.
Further, upper insulating layer 55 is formed on the inner edge of the lower surface of upper substrate 51 in a frame-like form. Lower insulating layer 56 is formed on the inner edge of the top surface of lower substrate 52 in a frame-like form. Upper bonding layer 57 is formed on the lower surface of upper insulating layer 55 in a frame-like form. Lower bonding layer 58 is formed on the top surface of lower insulating layer 56 in a frame-like form.
Wiring board 59 is further formed with a plurality of wiring patterns (not illustrated) on its top and lower surfaces, with upper and lower electrodes connected to the patterns. The respective outer parts of upper substrate 51 and lower substrate 52 are bonded each other by means of upper bonding layer 57 and lower bonding layer 58. Upper conductive layer 53 and lower conductive layer 54 are facing each other with certain air gap 60 provided to compose touch panel 50.
Touch panel 50 composed in this way is arranged on the front surface of a liquid crystal display element (not illustrated) or the like, to be attached to an electronic device. A pair of upper electrodes and a pair of lower electrodes are respectively connected to the electronic circuit (not illustrated) of the device through wiring board 59.
In the above-mentioned makeup, the top surface of upper substrate 51 is pressed by a finger, pen, or the like, while the display of the liquid crystal display element or the like on the back surface of touch panel 50 is viewed through touch panel 50. Consequently, upper substrate 51 deforms, causing upper conductive layer 53 corresponding to a position having been pressed to contact with lower conductive layer 54.
Then a voltage is applied sequentially to the upper and lower electrodes through wiring board 59 from the electronic circuit. The electronic circuit detects a position having been pressed owing to the voltage ratio between these electrodes, enabling various functions of the device to be selected.
Such a touch panel 50 is disclosed in Japanese Patent Unexamined Publication No. 2003-280821, for example.